Various combined rotary pump/rotary drive systems are known from the prior art, but such systems are invariably single-function systems in the sense that the pumping unit is not replaceable by a unit having a different hydraulic function, i.e. the impeller unit is either not replaceable without major engineering work, or is replaceable only with an identical or functionally similar impeller.
One such prior example is shown in U.S. Pat. No. 3,804,553 issued to Hickey where the impeller is a complex multi-component structure (FIG. 2) that cannot be removed and replace in one piece, but requires a long and complex series of painstaking assembly operations in the confined space of a one-piece rotor (FIGS. 3 to 13). Although Hickey refers to "a multiplicity of different fluid flow functions", it is clear from column 5, lines 34 to 50 that only hydrokinetic impellers with individually mounted blades are actually referred to (lines 36 to 37), all such impellers necessarily being assembled and demounted piece-by-piece through the open centre of a one-piece rotor tube. Hickey neither makes provision for nor suggests that impeller units can be assembled and removed as complete integral units, nor that hydrokinetic impellers could be substituted by hydraulic units of a quite different function that necessarily must be in a form not susceptible of being provided in a multitude of individual components smaller than the diameter of the assembled hydraulic unit and hence capable of passing through a one-piece rotor bore. In particular, Hickey provides only a one-piece rotor tube and neither suggests nor allows for half-shafts (see below) to allow the fitting of a selected one of a plurality of mechanically interchangeable but hydraulically functionally different rotary hydraulic machine units.